Many controllers for rod pumped oil and gas wells produce graphs called “dynographs” that plot the measured load on the rod against the position of the rod in the pumping stroke. An example of this type of graph is shown in FIG. 3. Inherent in the accuracy of this type of information is the accuracy of the measurement of the rod position. Currently, there are several mechanisms for measuring the rod position. One method uses Hall-effect transducers to model the position of the rod based on the geometry of the pump. Another method uses inclinometers mounted on the walking beam to detect the angle of the walking beam and derive a rod position from the angle. Other methods uses combinations of load sensors to measure beam flex and an inclinometer for beam angle to calculate rod position.
Each of these methods has inherent inaccuracies that can lead to inaccurate dynographs and data. What is needed is a more accurate mechanism for determining rod position in a pumping stroke.